1. Field of Invention
The present invention relates to light modules for motor vehicles and, more specifically, to light modules for headlamps of motor vehicles.
2. Description of Related Art
A light modules for a motor vehicle headlamp, as known in the art, is an assembly that alone, or in conjunction with other light modules of the same headlamp or at least one other headlamp, generates a light distribution in the foreground of a motor vehicle conforming to government-mandated regulations, when used as intended in a motor vehicle. The known light module has numerous light sources, a primary lens, and a secondary lens, wherein the primary lens is designed to collect light emitted from the light sources and to convert the light into an intermediate light distribution having the form of a closed illuminating surface area. The secondary lens has an object-side focal length, and the primary lens and the secondary lens are disposed such that the intermediate light distribution lies at a spacing of this focal length in the light path in front of the secondary lens. Intermediate light distributions from light modules that are intended to generate a light distribution having a light/dark border are bordered on at least one side by a sharp edge. The secondary lens is a lens or a reflector and has an object-side focal plane, which is distinguished in that the contours lying therein are mapped in a foreground of the light module lying behind the secondary lens in the direction in which the light is propagated.
Recently, semiconductor light sources, such as light emitting diodes (LED), have been used more frequently as light sources in motor vehicle headlamps. Initially, primarily (signal) lights for high-end vehicles have been operated with light emitting diodes, and the automotive industry is moving toward the use LEDs in conjunction with of low and high beam lights for mid-range vehicles as well. As a result of this development, there is a need in the art for inexpensive low and high beam light modules using LEDs as the light source. Powerful LED low beam light modules are typically designed as projection headlamps, where a two-stage lens first generates a real intermediate image of the light emission surface of the light emitting diodes used as the light sources. So-called arrays including numerous light emitting diodes are used in order to generate a sufficiently large luminous flux. The light emission surface of an individual LED used in such an array is, for example, quadratic, and has an edge length of approximately one millimeter, for example. The individual LEDs are disposed within the array such that their light emission surfaces border one another directly, substantially without any spacing, such that an overall light emission surface of the array that appears to be coherent is obtained. The disadvantage with these light modules, in particular, is the high price for the projection lens, and the expensive LED arrays.
Reflection systems in which a reflector generates a low beam light distribution in a single reflection (single-stage lens) are substantially simpler in terms of their assembly. The light distribution is formed as a superimposing of numerous elementary images of the light sources. The imaging of the light sources with an infinitesimally small reflector zone is understood to be the light source image. In order to superimpose the light source images to form a homogenous light distribution, the light source itself should likewise have a uniform light density. Furthermore, the light source requires a sharp border, the imaging of which generates the sharp light/dark border for the low beam light distribution. As a result, the simple, inexpensive reflection lens requires an expensive LED array as the light source.
However, instead of using an LED array having a basically closed light emitting surface, numerous individual LEDs disposed at a spacing to one another (e.g.: SMD-LEDs, SMD: surface mounted design) can be used, wherein gaps between the LED chips (and thus, in particular, between the light emission surfaces) result in dark stripes in the light distribution. Moreover, by blurring the resulting stripes in the light distribution with control lenses on the reflector surface in order to obtain a homogenous light distribution, the maximum illumination is reduced, at least in terms of the chip width in relation to the sum of the chip width and the chip spacing. Thus, the average light intensity of a blurred light source of this type is lower, in comparison to an array in which the LED chips are disposed directly adjacent to one another, at least in the specified relationship. Because of the tolerances of the individual chips, and in conjunction with the color converting phosphor, the sides of the LED chips never really lie on a line, which results in unclear light/dark borders in the imaging of the array.
As is the case with projection systems, the light/dark border is not generated through the imaging of an aperture shutter with reflection systems. Rather, the light/dark border is composed of light source images having different orientations, whereby in conventional reflection systems the focal point lies substantially lower than with projection systems (beneath the light/dark border). This has a negative effect on the range because the range decreases when the brightness of the bright region lying just below the light/dark border diminishes. Moreover, it is not possible to obtain the high luminosity gradients at the light/dark border with reflector systems that are typical of projection systems.
Thus, the objective of the invention is to provide a light module, which is as compact as possible, that can be operated with inexpensive SMD-LEDs, and that does not require an expensive and voluminous projection lens. Furthermore, the power of the light module, in relation to the luminosity at the edge of the light/dark border of a low beam light distribution, and in relation to the steepness of the gradients of the brightness curve at a right angle to the light/dark border, should reach the level obtained with projection modules.